1. Field of the Art
The present invention relates to a polishing composition for aluminum disks having a SiO2 concentration of 0.5 to 50% by weight containing colloidal silica particle groups having different monomodal numerical particle size distribution therein or substrates having silica on the surface thereof, in order to obtain a polished surface having a smaller mean waviness.
Here, the polishing of aluminum disks referred to herein means polishing the surface of the substrate itself of a magnetic memory disk composed of aluminum or its alloy, or polishing the surface of the nickel-phosphorus (Nixe2x80x94P) or nickel-boron (Nixe2x80x94B) plating, especially a hard layer of non-electrolysis nickel-phosphorus (Nixe2x80x94P) plating composing of 90 to 92% of Ni and 8 to 10% of P, and aluminum oxide layer on the substrate.
Polishing of the substrate with silica on the surface thereof means polishing the surface layer on the substrate containing 50% or more by weight of silica. Examples of such polishing include polishing rock crystal, quartz glass for photomasks, silicon oxide films on semiconductor devices, crystallized glass-made hard disks, and either aluminosilicate glass- or soda lime glass-made hard disks.
Since the polishing composition of the present invention can efficiently give smooth polished surfaces with high precision, it is also useful for the precision polishing of semiconductor wafers made of silicon alone, semiconductors wafers made of chemical compounds such as gallium arsenide, gallium phosphide or indium phosphide, and interconnecting metals such as copper and aluminum for semiconductor multi level interconnection substrates, nitride films and carbide films and the like, as well as for final polishing of single crystals of sapphire, lithium tantalate, lithium niobate and the like, and GMR magnetic head among others.
2. Description of the Related Art
Sols composed of highly stable colloidal silica particles as the silica sol have been used in part or under consideration for use in the final polishing of aluminum disks, glass disks, quartz glass for photomasks, rock crystal, siliceous substrate such as silicon oxide films for semiconductor devices, semiconductor wafers, single crystals such as sapphire, lithium tantalate and lithium niobate, MR magnetic head and the like. However, it has been pointed out that silica sol has a shortcoming in low removal rate in spite of attaining highly satisfactory polished surface having a good mean surface roughness.
The object of the present invention is to provide a polishing composition for aluminum disks and glass-made disks, quartz glass, rock crystal as well as silicon oxide films for semiconductor devices in view of solving low removal rate and giving polished surface of excellent quality. In particular, the disk is likely to be rotated at an increased rotation speed with the decreased gap between the disk and the magnetic head in order to meet the increase in the density of memory capacity in the case of aluminum disks and glass-made hard disks, and furthermore, disks with less mean waviness are being desired in recent days.
In particular, more rigorous requirements for mean waviness are being asked for aluminum disks and glass-made hard disks in order to meet the increase in the density of memory capacity leading to faster rotation of the disk with the decreased gap between the disk and the magnetic head. Recently, disks having a mean waviness of less than 3 xc3x85 are being desired.
Here, the present invention was accomplished in making a polishing composition containing colloidal silica particles with a SiO2 concentration of 0.5 to 50% by weight by the use of a water dispersed stable silica sol containing colloidal silica particle groups having two or three types of different monomodal numerical particle size distributions with the ratio of the mean particle size (particle size measured with the nitrogen adsorption method) being 0.15 to 0.80 mixed with SiO2 with the weight ratio of 1:0.05 to 9.0, and in obtaining an aluminum disk or a substrate having silica on the surface thereof of good quality.
The measured particle size of colloidal silica particle group determined with the nitrogen adsorption method can be obtained according to the formula D=2720/S (nm) from the specific surface area S (m2/g) measured with the nitrogen adsorption method.
More specifically, the first embodiment of the instant invention relates to a polishing composition for an aluminum disk comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 80 to 120 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Da (particle size measured with the nitrogen adsorption method) in the range of 65 to 100 nm (referred as colloidal silica particle group (a) hereinafter), and
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 20 to 40 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dc (particle size measured with the nitrogen adsorption method) in the range of 15 to 25 nm (referred as colloidal silica particle group (c) hereinafter),
wherein said composition has the ratio of Dc/Da of 0.15 to 0.38, contains a water dispersed stable silica sol mixed as SiO2 with the weight ratio of said colloidal silica particle group (a) to said colloidal silica particle group (c) of W(a):W(c)=1:0.05 to 9.0, and contains colloidal silica particles with the SiO2 concentration of 0.5 to 50% by weight.
The second embodiment of the instant invention relates to a polishing composition for an aluminum disk containing silica sol comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 80 to 120 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Da (particle size measured with the nitrogen adsorption method) in the range of 65 to 100 nm (referred as colloidal silica particle group (a) hereinafter),
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 20 to 40 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dc (particle size measured with the nitrogen adsorption method) in the range of 15 to 25 nm (referred to as colloidal silica particle group (c) hereinafter), and
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 5 to 15 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dd (particle size measured with the nitrogen adsorption method) in the range of 8 to 12 nm (referred as colloidal silica particle group (d) hereinafter),
wherein said composition has the ratio of Dc/Da of 0.15 to 0.38 and the ratio of Dd/Dc of 0.26 to 0.80, contains a water dispersed stable silica sol mixed as SiO2 with the weight ratio of said colloidal silica particle group (a), said colloidal silica particle group (c) and said colloidal particle group (d) being W(a):W(c):W(d)=1:0.05 to 9.0:0.01 to 1.4, and contains colloidal silica particles with the SiO2 concentration of 0.5 to 50% by weight.
The third embodiment of the instant invention relates to a polishing composition for an aluminum disk containing silica sol comprising of
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 40 to 70 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Db (particle size measured with the nitrogen adsorption method) in the range of 35 to 50 nm (referred as colloidal silica particle group (b) hereinafter), and
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 20 to 40 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dc (particle size measured with the nitrogen adsorption method) in the range of 15 to 25 nm (referred as colloidal silica particle group (c) hereinafter) or
a colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of 5 to 15 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dd (particle size measured with the nitrogen adsorption method) in the range of 8 to 12 nm (referred as colloidal silica particle group (d) hereinafter),
wherein said composition has the ratio of Dc/Db of 0.30 to 0.71 or the ratio of Dd/Db of 0.16 to 0.34, contains a water dispersed stable silica sol mixed as SiO2 with the weight ratio of said colloidal silica particle group (c) or said colloidal silica particle group (d) and said colloidal particle group (b) being W(b):[W(c) or W(d)]=1:0.05 to 9.0, and contains colloidal silica particles with the SiO2 concentration of 0.5 to 50% by weight.
The polishing compositions according to the first to third embodiments are used in polishing aluminum disks and substrates having silica on the surface thereof.
Here, high speed polishing property is also necessary as one of required properties for polishing compositions in order to obtain disks with small mean waviness. Accordingly, the addition of one or more kinds of aluminum compounds selected from the group consisting of aluminum nitrate, aluminum sulfate, aluminum chloride, basic aluminum nitrate and basic aluminum sulfamate, and one or more kinds of iron compounds selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, and iron (III) potassium sulfate [KFe(SO4)2] as polishing accelerators to the polishing composition of the present invention enables to achieve the high speed polishing.
Aluminum compounds as well as carboxylic acids with the stabilizing effect for trivalent iron compounds such as maleic acid, tartaric acid, citric acid, malic acid, gluconic acid or lactic acid may be added in view of getting accelerating effects in polishing and stabilizing polishing properties.
In the present invention, if the ratio of mean particle sizes (particle sizes measured with the nitrogen adsorption method) for colloidal silica particle groups having different monomodal numerical particle size distributions is less than 0.15, the improving effect for the polishing property of the polishing composition is small. Similarly, if the ratio of mean particle size (particle size measured with the nitrogen adsorption method) is greater than 0.80, the improving effect for the polishing property of the polishing composition is also small.
In the present invention, if the smaller colloidal silica particle group among the colloidal silica particle groups having different monomodal numerical particle size distributions has the SiO2 ratio by weight of less than 0.05, the improving effect for the polishing property of the polishing composition is small. Similarly, if it has the SiO2 ratio by weight of more than 9.0, the improving effect for the polishing property of the polishing composition is small as well.
The polishing composition of the present invention may be mixed with colloidal silica particle group having a monomodal numerical particle size distribution with primary particle sizes of more than 150 nm but less than 250 nm as observed on a transmission electron microscope being 90% or more of the total particle number, and having a mean particle size Dx (particle size measured with the nitrogen adsorption method) in the range of 100 to 140 nm.
The content of the colloidal silica particle group in the polishing composition of the present invention is 0.2 to 50% by weight, preferably 1 to 30% by weight as SiO2 concentration. If the SiO2 concentration is less than 0.2% by weight, the effect on the polishing is small, and if the SiO2 concentration is more than 50% by weight, the sol becomes unstable.
Although the silica sol may be used as an alkaline sol as it is in polishing aluminum disks, sols obtained by treating alkaline sols with a cation exchange or sols obtained by rendering acidic with the addition of a water soluble acidic substance such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid or oxalic acid are more preferred.
Also, aluminum nitrate, aluminum sulfate, aluminum chloride, basic aluminum nitrate or basic aluminum sulfamate among others as the polishing accelerator may be used and its content is preferably 0.01 to 5.0% by weight as Al2O3 concentration. If this content is less than 0.01% by weight as Al2O3 concentration, the effect on the polishing is small, and if it is more than 5.0% by weight, the silica sol becomes unstable.
Iron compound such as iron (III) nitrate, iron (III) chloride, iron (III) sulfate or iron (III) potassium sulfate may be used as the polishing accelerator, and its content is preferably 0.01 to 5.0% by weight as Fe2O3 concentration. If the content is less than 0.01% by weight as Fe2O3 concentration, the effect of accelerating on the polishing is small, and if it is more than 5.0% by weight, the silica sol becomes unstable.
Further, the content of carboxylic acid such as maleic acid, tartaric acid, citric acid, malic acid, gluconic acid or lactic acid is preferably 0.01 to 5.0% by weight. If it is less than 0.1% by weight, the effect as polishing accelerator and stabilizing agent is small, and if it is more than 5.0% by weight, the silica sol becomes unstable.
Furthermore, metal salt such as nickel nitrate, zirconyl nitrate, cerium nitrate or ammonium molybdate among others may be added as the polishing accelerator.
The alkaline silica sols may be used as they are, after they are subjected to a cation exchange treatment or rendered acidic with the addition of a water soluble acidic substance such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid or phosphoric acid among others in a method for polishing glass-made hard disks.
Further, alumina, zirconia, zirconium silicate, mullite, cerium oxide, iron oxide, chromium oxide, titanium oxide or tin oxide among others may be added to the polishing composition of the present invention, and hydrated oxides such as aluminum hydroxide, boehmite and goethite as well as non-oxides such as diamond, boron nitride, silicon nitride and silicon carbide may also be added.
Water soluble alcohols such as ethanol, propanol, ethylene glycol and propylene glycol, surface active agents such as sodium alkylbenzenesulfonate and formalin condensate, organic substances of poly-anionic series such as polyacrylic acid salt, and celluloses such as cellulose, hydroxyethyl cellulose and carboxymethyl cellulose, which are generally added to polishing compositions may also be added.